Toroidal type continuously variable transmission

ABSTRACT

A toroidal type continuously variable transmission, includes: at least one pair of disks concentrically disposed on each other and rotatably supported independent from each other; a trunnion swingable about a pivot shaft; a displacement shaft including a support shaft portion and a pivot shaft portion that are parallel and eccentric to each other, the support shaft portion rotatably supported to the circular hole of the trunnion through a radial bearing, the pivot shaft portion being protruded from an inner surface of the middle portion of said trunnion; a power roller nipped between the concave surfaces of the pair of disks while being rotatably supported on an outer circumferential surface of the pivot shaft portion; and a thrust bearings located between the power roller and the inner surface of the middle portion of the trunnions. An eccentric quantity of the displacement shaft being a distance between the support shaft portion and the pivot shaft portion is within a range from 5 mm to 15 mm.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a toroidal type continuouslyvariable transmission which may be used as a transmission unitconstituting a vehicular transmission or may be assembled astransmissions into various types of industrial machines.

[0003] 2. Description of the Related Art

[0004] Study on the application of a toroidal type continuously variabletransmission (as shown in FIGS. 1 and 2 ) into a vehicular transmissionprogresses. An example of the toroidal type continuously variabletransmission is disclosed in Japanese Utility Model UnexaminedPublication Sho.62-71465.

[0005] In a conventional toroidal type continuously variabletransmission shown in FIGS. 1 and 2, an input-side disk 2 isconcentrically supported to an input shaft 1. An output shaft 3 is alsodisposed concentrically with an input shaft 1. An output-side disk 4 isfastened to the inner end of the output shaft 3. In the inside of acasing in which the toroidal type continuously variable transmission isstored, there are located a pair of trunnions 6, 6 at an intermediateposition of the both disks 2, 4 along the axial direction thereof. Thetrunnions 6, 6 are swingable about their respective pivot shafts 5, 5respectively disposed at position along an imaginary plane that isperpendicular to an imaginary line connecting the respective axes of theinput and output shafts 1 and 3, and distanced from the intersection ofthe imaginary plane and imaginary line, as shown in FIG. 1. Thisphysical relation is hereinafter referred to as “torsional relation”.

[0006] Each of the trunnions 6, 6 located distant from the center axisof the input-side disk 2 and the output-side disk 4 is concentricallyprovided with each of the pivot shafts 5, 5 on the outer side surfacesof the two end portions thereof. The base end portions of displacementshafts 7, 7 are respectively supported in the central portions of thetrunnions 6, 6 and if the trunnions 6, 6 are swung about the pivotshafts 5, 5 respectively, the inclination angles of the displacementshafts 7, 7 can be adjusted freely. On the peripheries of the twodisplacement shafts 7, 7 supported on the two trunnions 6, 6, there arerotatably supported a plurality of power rollers 8, 8 respectively. Thepower rollers 8, 8 are respectively interposed between the innersurfaces 2 a and 4 a, opposed to each other, of the input-side disk 2and the output-side disk 4. The inner surfaces 2 a and 4 a are formed asconcave surfaces which can be obtained by rotating an arc having thepivot shaft 5 as a center thereof. And, the peripheral surfaces 8 a, 8 aof the power rollers 8, 8, which are formed as spherical-shaped convexsurfaces are respectively in contact with the inner surfaces 2 a and 4a.

[0007] Between the input shaft 1 and input-side disk 2, there isinterposed a pressure device 9 of a loading cam type, while theinput-side disk 2 is elastically pressed toward the output-side disk 4by the pressure device 9. The pressure device 9 is composed of a camplate 10 rotatable together with the input shaft 1, and a plurality of(for example, four pieces of) rollers 12, 12 which are respectivelyrollably held by a retainer 11.

[0008] On one side surface (in FIGS. 1 and 2, on the left side surface)of the cam plate 10, there is formed a drive-side cam face 13 being acurved surface which extends over the circumferential direction of thecam plate 10. And, on the outer surface (in FIGS. 1 and 2, on the rightside surface) of the input-side disk 2, there is also formed adriven-side cam face 14 having a similar shape. The plurality of rollers12, 12 are each rotatably supported about their respective shafts whichextend in the radial direction with respect to the center of the inputshaft 1.

[0009] The above-structured toroidal type continuously variabletransmission operates in the following way. When the cam plate 10 isrotated with the rotation of the input shaft 1, the drive-side cam face13 presses the plurality of rollers 12, 12 against the driven-side camface 14 formed on the outer surface of the input-side disk 2. As aresult of this, the input-side disk 2 is pressed against the pluralityof power rollers 8, 8 and, at the same time the drive-side anddriven-side cam faces 13 and 14 are pressed against the plurality ofrollers 12, 12, so that the input-side disk 2 is rotated. The rotationof the input-side disk 2 is transmitted through the plurality of powerrollers 8, 8 to the output-side disk 4, so that the output shaft 3fastened to the output-side disk 4 is rotated.

[0010] Next, a description will be given of a case of changing of arotational speed ratio (speed change ratio) of the input and outputshafts 1 and 3. At first, when decelerating the rotational speed betweenthe input shaft 1 and the output shaft 3, the trunnions 6, 6 are swungabout the pivot shafts 5, 5 in a predetermined direction, respectively.Then, the displacement shafts 7, 7 are respectively inclined so that theperipheral surfaces 8 a, 8 a of the power rollers 8, 8, as shown in FIG.1, can be respectively contacted with a near-center portion on the innersurface 2 a of the input-side disk 2 and with a near-outer-peripheryportion on the inner surface 4 a of the output-side disk 4.

[0011] Also, on the other hand, when accelerating the rotational speedbetween the input and output shafts 1 and 3, the trunnions 6, 6 arerespectively swung about the pivot shafts 5, 5 in the opposite directionto the predetermined direction. Then, the displacement shafts 7, 7 arerespectively inclined so that the peripheral surfaces 8 a, 8 a of thepower rollers 8, 8, as shown in FIG. 2, can be respectively contactedwith a near-outer-periphery portion on the inner surface 2 a of theinput-side disk 2 and a near-center portion on the inner surface 4 a ofthe output-side disk 4. When the inclination angles of the displacementshafts 7, 7 are set in the middle of the inclination angles shown inFIGS. 1 and 2, then there can be at obtained an intermediatetransmission ratio between the input and output shafts 1 and 3.

[0012] A specific example of the toroidal type continuously variabletransmission is shown in FIGS. 3 and 4. This transmission is disclosedin Japanese Utility Model Unexamined Publication No. Hei. 1-173552,recorded in a microfilm. As shown, an input-side disk 2 and anoutput-side disk 4 are rotatably supported around a cylindrical inputshaft 15 with the aid of needle roller bearings 16, 16 insertedtherebetween. A cam plate 10 is spline engaged with the outer peripheralsurface of the end portion (in FIG. 3, the left end portion) of theinput shaft 15 and is prevented, by a flange portion 17, from moving ina direction away from the input-side disk 2. Further the cam plate 10and rollers 12, 12 constitute a pressure device 9 of a loading cam type.The pressure device 9, in accordance with the rotation of the inputshaft 15, rotates the input-side disk 2 while it is pressing against theinput-side disk 2 toward the output-side disk 4. An output gear 18 iscoupled to the output-side disk 4 by means of keys 19, 19 so that theoutput-side disk 4 and the output gear 18 are synchronously rotated.

[0013] A pair of trunnions 6, 6, in particular, their respective two endportions thereof are supported on a pair of support plates 20, 20 insuch a manner that they can be swung and can be displaced in the axialdirection (in FIG. 3, in the front and back direction, or in FIG. 4, thehorizontal directions) thereof. And, two displacement shafts 7, 7 arerespectively supported in circular holes 21, 21 which are respectivelyformed in the middle portions of the pair of trunnions 6, 6. The twodisplacement shafts 7, 7 respectively include support shaft portions 22,22 and pivot shaft portions 23, 23 which are extend in parallel to eachother but are eccentric to each other. The support shaft portions 22, 22are rotatably supported inside the circular holes 21, 21 through radialneedle roller bearings 24, 24, respectively. Also, power rollers 8, 8are rotatably supported in the peripheries of the pivotal supportportions 23, 23 through another radial needle roller bearings 25, 25,respectively.

[0014] As shown in FIGS. 5 and 6 in detail, each of the radial needleroller bearings 25, 25 is constructed with a plurality of needle rollers45, 45 and cage-like window type retainers 53 for holding rollably thoseneedle rollers 45, 45. In this case, the outer circumferential surfaceof the pivot shaft portion 23 serves as a cylindrical inner raceway 54of the radial needle roller bearing 25, and the inner circumferentialsurface of the power roller 8 serves as the outer raceway 55 of theradial needle roller bearing 25.

[0015] The pair of the displacement shafts 7, 7 are respectivelydisposed on 180 deg.-separated opposite sides with respect to the inputshaft 15. Also, a direction, in which the pivot shaft portions 23, 23 ofthe displacement shafts 7, 7 are eccentric to the support shaft portions22, 22, is set as the same direction with respect to the rotationdirection of the input- and output-side disks 2 and 4. Also, theeccentric direction is set almost at right angles to the direction inwhich the input shaft 15 is disposed. Therefore, the power rollers 8, 8are supported in such a manner that they can be somewhat displaced inthe disposing direction of the input shaft 15. As a result, even when,due to accumulation of the dimensional tolerance of the componentsparts, the input- and output-side disks 2 and 4 are displaced from thetrunnions 6, 6 in the axial direction of the input shaft 15 (in FIG. 3,the horizontal direction, or in FIG. 4, front-back direction) to somedegree, adequate contact of the inner surface 2 a and the inner surface4 a of the disks 2 and 4 with the peripheral surfaces 8 a of the powerrollers 8 is secured. Further, when the component parts are deformed bylarge loads imparted thereto in a transmission state of the rotationalforce, and as a result of the deformation, even if the power rollers 8,8 are likely to displace in the axial direction of the input shaft 15,this displacement of the power rollers 8, 8 may be absorbed withoutapplying excessive force to the component parts.

[0016] Also, between the outer surfaces of the power rollers 8, 8 andthe inner surfaces of the middle portions of the trunnions 6, 6, thereare interposed thrust ball bearings 26, 26 and thrust needle rollerbearings 27 are disposed in this order from the outer surfaces of thepower rollers 8. The thrust ball bearing 26, 26 are respectively used toallow the power rollers 8, 8 to rotate while supporting the load appliedto the power rollers 8, 8 in the thrust direction. The thrust ballbearings 26, 26 are respectively composed of a plurality of balls 56, 56annular-shaped retainers 57, 57 for rollably holding the balls 56, 56therein, and annular-shaped outer races 28, 28. The inner raceways ofthe thrust ball bearings 26, 26 are respectively formed on the outersurfaces of the power rollers 8, 8, whereas the outer raceways thereofare respectively formed on the inner surfaces of the outer races 28, 28.

[0017] Each of the thrust needle roller bearings 27, 27 is composed of arace 58, a retainer 59 and needle rollers 60, 60. The race 58 andretainer 59 are combined together in such a manner that they can besomewhat displaced in the rotation direction. The thrust needle rollerbearings 27, 27 interpose the races 58, 58 between the inner surfaces ofthe trunnions 6, 6 and the outer surfaces of the outer races 28, 28 in astate that the races 58, 58 are contacted with the inner surfaces of thetrunnions 6, 6. The thrust needle roller bearings 27, 27 allow the pivotshaft portions 23, 23 and the races 28, 28 to rotate about the supportshaft portions 22, 22 while receiving a thrust load applied to the outerraces 28, 28.

[0018] Drive rods 29, 29 are respectively coupled to one end portions(left end in FIG. 4) of the trunnions 6, 6. And, drive pistons 30, 30are respectively firmly coupled to the outer surface of the middleposition of the drive rods 29, 29. The drive pistons 30, 30 areoil-tightly disposed within drive cylinders 31, 31. An amount ofdisplacement of each of the trunnions 6, 6, which is caused by supplyingoil into and discharging it from each of the drive cylinders 31, 31 isdetected by a precess cam (not shown) fixed to the other end portions ofthe trunnions 6, 6.

[0019] A lubricating-oil supplying device as shown in FIG. 7 is providedin the insides of the drive rod 29, the trunnion 6 and the displacementshaft 7. The lubricating-oil supplying device feeds a sufficient amountof lubricating oil into the bearings 25 and 26 in order to secure thedurability of the radial needle roller bearing 25 and the thrust ballbearing 26. The lubricating-oil supplying device is composed of afeeding-side oil-supply passage 42 provided in the insides of the driverod 29 and the trunnion 6, oil-feedholes 43, 43 formed in the outer race28 of the thrust ball bearing 26, and a receiving-side oil-supplypassage 44 provided in the inside of the pivot shaft portion 23, whichconstitutes the first half of the displacement shaft 7. When thetoroidal type continuously variable transmission is in operation, thelubricating-oil supplying device feeds lubricating oil into thefeeding-side oil-supply passage 42 with the aid of a pump (not shown)assembled into the transmission, to thereby lubricate the bearings 25and 26.

[0020] In the thus constructed toroidal type continuously variabletransmission, a rotation of the input shaft 15 is transmitted to theinput-side disk 2 through the pressure device 9. A rotation of theinput-side disk 2 is transmitted through the pair of power rollers 8, 8to the output-side disk 4, and a rotation of the output-side disk 4 isoutput from the output gear 18. To change the rotational speed changeratio between the input shaft 15 and the output gear 18, the pair ofdrive pistons 30, 30 are displaced in the opposite directions to eachother. In accordance with the displacement of the drive pistons 30, 30,the pair of trunnions 6, 6 displace in the opposite directions, so thatthe lower power roller 8 disposed in the downside of FIG. 4 displaces tothe right, while at the same time the upper power roller 8 disposed inthe upside of FIG. 4 displaces to the left. Accordingly, the directionof forces in the tangential direction which act on contact positionswhere the peripheral surfaces 8 a, 8 a of the power rollers 8, 8 are incontact with the inner surface 2 a of the input-side disk 2 and theinner surface 4 a of the output-side disk 4, is changed. In accordancewith the changing of the direction of the forces, the trunnions 6, 6 areswung about the pivot shafts 5, 5 which are supported by the supportplates 20, 20 in the opposite directions to each other. As a result, asshown in FIGS. 1 and 2, the contact positions where the peripheralsurfaces 8 a, 8 a of the power rollers 8, 8 are in contact with theinner surface 2 a and the inner surface 4 a of the input- andoutput-side disks 2 and 4 are shifted, whereby the rotational speedchange ratio between the input shaft 15 and the output gear 18 ischanged. The control of the rotational speed change ratio to a desiredvalue is conducted in a manner that the amounts of the displacements ofthe trunnions 6, 6 in the axial directions of the pivot shafts 5, 5,which are detected by the precess cam, is adjusted by adjusting theamounts of the pressurized oil charged to and discharged from the drivecylinders 31, 31.

[0021] When the rotational force is transmitted between the input shaft15 and the output gear 18, based on the elastic deformation of thecomponent parts, the power rollers 8, 8 are displaced in the axialdirection of the input shaft 15. As a result, the displacement shafts 7,7 which pivotally support the power rollers 8 are slightly turned aboutthe support shaft portions 22, respectively. Due to the turning of thedisplacement shafts 7, 7, the outer surfaces of the outer races 28, 28of the thrust ball bearings 26, 26 are displaced relative to the innersurfaces of the trunnions 6, 6. A force required for the relativedisplacement is small because the thrust needle roller bearings 27 arepresent between the outer surfaces of the races 28, 28 and the innersurfaces of the trunnions 6, 6. This fact implies that a force to changean inclination angle of each of the displacement shafts 7, 7 is small.

[0022] Turning now to FIGS. 8 and 9, there are shown toroidal typecontinuously variable transmissions increased in their transmissibletorque. As shown, a couple of input disks 2A and 2B and a couple ofoutput disks 4, 4 are arranged side by side around an input shaft 15 ain the power transmission direction. In either structure (FIGS. 8 and9), an output gear 18 a is disposed in a middle portion of the inputshaft 15 a to be rotatably supported around the input shaft 15 a. Theoutput disks 4, 4 are spline-engaged to both ends of a cylindricalsleeve 32 provided in the central portion of the output gear 18 a.Needle roller bearings 16, 16 are respectively provided between theinner circumferential surfaces of the output disks 4, 4 and the outercircumferential surface of the input shaft 15 a. With provision of theneedle roller bearings 16, the output disks 4, 4 are supported aroundthe input shaft 15 a so as to be rotatable about the input shaft 15 aand movable in the axial direction of the input shaft 15 a. The inputdisks 2A and 2B are supported at both ends of the input shaft 15 a whilebeing rotatable together with the input shaft 15 a. The input shaft 15 ais rotatable driven by a drive shaft 33 through the pressure device 9 ofthe loading cam type. There is provided a radial bearing 34, such as asliding bearing or a needle roller bearing, is disposed between theouter circumferential surface of the tip end (right end of in FIGS. 8and 9) of the drive shaft 33 and the inner circumferential surface ofthe base end (left end in FIGS. 8 and 9) of the input shaft 15 a.Therefore, the drive shaft 33 and the input shaft 15 a areconcentrically combined with each other such that those shafts areslightly movable in the rotational direction.

[0023] The rear surface of input-side disk 2A (located on the right sidein FIGS. 8 and 9) is thrust against a loading nut 35 directly (in thestructure shown in FIG. 9) or with a coned disk spring 36 having largeresilience being interposed therebetween (in the structure shown in FIG.8), to thereby substantially prevent the displacement of the input-sidedisk 2A in the axial directions (horizontal directions in FIGS. 8 and 9)of the input shaft 15 a. On the other hand, the input-side disk 2Bfacing the cam plate 10 is supported to be movable in the axialdirection of the input shaft 15 a with the aid of a ball spline 37. Aconed disk spring 38 and a thrust needle roller bearing 39 are seriallydisposed between the rear surface (right-side surface in FIGS. 8 and 9)of the input-side disk 2B and the front surface (right-side surface inFIGS. 8 and 9) of the cam plate 10. The coned disk spring 38 functionsso as to impart pre-load to contact portions where the inner surfaces 2a of the input-side disks 2A and 2B and the inner surface 4 a of theoutput-side disk 4 are in contact with the peripheral surfaces 8 a, 8 aof the power rollers 8, 8. The thrust needle roller bearing 39 allowsthe input-side disk 2B to rotate relative to the cam plate 10 when thepressure device 9 operates.

[0024] In the structure of FIG. 8, the output gear 18 a is rotatablysupported while the axial displacement thereof being prevented, on apartitioning wall 40 provided inside of the housing, by a pair of ballbearings 41, 41 of the angular type. In the structure of FIG. 9, theoutput gear 18 a is axially displaceable. In the toroidal typecontinuously variable transmission of the double cavity type in whichthe couple of input-side disks 2A and 2B and the couple of output-sidedisks 4, 4 are arranged side by side in the power transmissiondirection, as shown in FIGS. 8 and 9, one of the input-side disks 2A and2B, which faces the cam plate 10 or both of them is or are axiallymovable with respect to the input shaft 15 a by means of the ball spline37, 37 a. The reason for this is that the transmission structure isdesigned so as to allow the input-side disks 2A and 2B to displace inthe axial directions of the input shaft 15 a, while securing thesynchronous rotations of the input-side disks 2A and 2B, based on theelastic deformation of the related component parts due to operations ofthe pressure device 9.

[0025] The ball spline 37 and ball spline 37 a include inner-diameterball-spline grooves 62 formed in the inner circumferential surfaces ofthe input-side disks 2A and 2B, outer-diameter ball-spline grooves 63formed in the outer circumferential surfaces of the intermediate portionof the input shaft 15 a, and a plurality of balls 64, 64 rollablyprovided between the inner-diameter ball-spline grooves 62 and theouter-diameter ball-spline grooves 63. As for the ball spline 37 forsupporting the input-side disk 2B located closer to the pressure device9, a stopper ring 66 is retained in a stopper groove 65 formed in aportion of the inner circumferential surface of the input-side disk 2B,which is closer to the inner surface 2 a thereof, to thereby limit theballs 64, 64 in displacing toward the inner surface 2 a of theinput-side disk 2B. Further, it prevents the balls 64, 64 from slippingoff from between the inner-diameter ball-spline grooves 62 and theouter-diameter ball-spline grooves 63. As for the ball spline 37 a forsupporting the input-side disk 2A located apart from the pressure device9 in the transmission structure of FIG. 8, a stopper ring 66 a isretained in a stopper groove 65 a formed in the outer circumferentialsurface (a portion thereof closer to the left end in FIG. 8) of theinput shaft 15 a, to thereby limiting the balls 64, 64 in displacingtoward the inner surface 2 a of the input-side disk 2A.

[0026] In the known or proposed toroidal type continuously variabletransmission, less consideration is given to the eccentric quantities ofthe displacement shafts 7, 7 for supporting respectively the powerrollers 8, 8 on the inner surfaces of the intermediate portions of thetrunnions 6, 6. The support shaft portion 22, 22 and the pivot shaftportion 23, 23 are parallel to each other, but the former is eccentricfrom the latter, viz., their centers are not coincident with each other(FIGS. 13, 24 and 25). Little qualitative consideration has been made onan eccentric quantity L₇ present between the support shaft portion andthe pivot shaft portion 23, 23. The study by inventor(s) on the toroidaltype continuously variable transmission showed the following fact: Toextract desired performances of the toroidal type continuously variabletransmission, it is essential to place the eccentric quantity L₇ withina proper range of eccentric quantity values. This fact will be describedby use a case where the toroidal type continuously variable transmissionof the double cavity type as shown in FIG. 10 is in a maximumdeceleration state where trouble occurrence is most frequent.

[0027] When the eccentric quantity L₇ is excessively small, the speedchange ratio of the toroidal type continuously variable transmissionshifts from a desired speed change ratio for the following reason. Toabsorb the dimensional tolerance of the component parts and the elasticdeformations of those parts during the power transmission, the pivotshaft portion 23 constituting each displacement shafts 7 revolves aroundthe support shaft portion 22. For example, at the time of thetransmission of power, a thrust load that is generated by the pressuredevice 9 thrusts the output-side disk 4. The output-side disk 4 iselastically displaced from a position (dot chain line in FIG. 11) toanother position (solid line in FIG. 11), and the input-side disk 2B isdisplaced toward the output-side disk 4 (right side in FIG. 11). Inaccordance with the displacement, the power roller 8 held between theinner surface 2 a of the input-side disk 2B and the inner surface 4 a ofthe output-side disk 4 moves in the axial direction (referred to as anx-direction, for ease of explanation) of the input shaft 15 a. With themovement, the trunnion 6, the displacement shaft 7 and the power roller8 changes from their disposition of FIG. 12A to another disposition ofFIG. 12B. The change of the disposition of those components results fromthe revolution of the pivot shaft portion 23 with respect to the supportshaft portion 22. Therefore, the pivot shaft portion 23 and the powerroller 8 move also in the axial direction (referred to as a y-direction,for ease of explanation) of the pivot shafts 5, 5 which pivotallysupports the trunnion 6 as well as in the x-direction, as shown in FIGS.13A and 13B.

[0028] The movement of the pivot shaft portion 23 and the power roller 8in the y-direction, as seen from the above description, is the same asthe operation of them in a case where the trunnions 6 are displaced inthe axial direction of the pivot shafts 5, 5 by moving forward andbackward the drive rods 29 (see FIG. 4) to change an inclination angleof the power roller 8 for the purpose of changing the rotational speedchange ratio of the input-side disk 2B and the output-side disk 4.Accordingly, when the power roller 8 displaces in the x-direction, onthe basis of the displacement in the y-direction which is simultaneouslyapplied, the power roller 8 is displaced by a distance corresponding tothe displacement in the y-direction caused by the revolution, althoughthe trunnion 6 per se does not displace in the y-direction. When adegree of speed change (speed change quantity), which is caused by sucha displacement of the power roller is small, no problem arises. When itis too much large, the speed change ratio cannot be controlled asdesired.

[0029] To control the speed change ratio of the toroidal typecontinuously variable transmission, a controller decides a target speedchange ratio based on a signal representative of throttle-valveposition, engine speed, or running speed; an instruction signalindicative of the target speed change ratio is applied to a relatedelectric motor; and controls the switching of a hydraulic-pressurecontrol valve, and thus operates the drive pistons 30 (FIG. 4). And, thecontact positions where the peripheral surfaces 8 a of the power rollers8 are in contact with the inner surface 2 a of the input-side disk 2(2A, 2B) and the inner surface 4 a of the output-side disk 4 are shiftedto other positions, so as to change the inclination angles of the powerrollers 8. However, where a quantity y8 of a displacement of the powerroller 8 in the y-direction, caused by the revolution motion, isincreased, another action not caused by the signals stated above existsin addition to the action for the changing of the speed change ratio,which is caused by the drive pistons 30, 30. Therefore, the toroidaltype continuously variable transmission changes its speed change ratio.Further, an actual speed change ratio is greatly deviated from thetarget one, and the toroidal type continuously variable transmissionoperates in a region out of an optimum region of its characteristicwhere the fuel consumption by the engine is efficient and the outputpower of the engine is high. This situation should be avoided.

[0030] In the conventional technique, it is considered that thepreferable way to suppress the y-directional movement of the powerroller 8, which is produced when the power roller 8 is moved in thex-direction is to secure the eccentric quantity L₇ of the support shaftportions 22, 22 from the pivot shaft portions 23, 23 as large aspossible. Further, it is recognized that where the eccentric quantity L₇is excessively large, a cross sectional area of the joint portion wherethe support shaft portions 22, 22 and the pivot shafts portions 23, 23are jointed together is small, and as a result, a stress generated inthe joint portion is great and in this condition it is very difficult tosecure a satisfactory durability of the displacement shafts 7, 7.Therefore, the designer considers that the eccentric quantity L₇ hascertain values of the upper limit, and they determine the eccentricquantity L₇ on the basis of the best balance between the securing of thedurability of the displacement shaft and the suppressing of they-directional component.

[0031] As described above, the conventional design of the eccentricquantity L₇ between the support shaft portions 22, 22 and the pivotshaft portions 23, 23 constituting the displacement shafts 7, 7 is notbased on definite rules constructed in consideration with theperformance on the speed-ratio change of the toroidal type continuouslyvariable transmission. The inventor(s) discovered that there is aspecific correlation between the eccentric quantity L₇ and thespeed-ration change performance of the toroidal type continuouslyvariable transmission, and that the eccentric quantity L₇ with aspecific range, provides a satisfactory speed-ratio change performance.

[0032] Further, in designing the conventional toroidal type continuouslyvariable transmission, any special consideration has been given to thesurface natures of the displacement shafts 7 which are used forsupporting the power rollers 8, 8 on the trunnions 6, 6 in rotatable anddisplaceable fashion. Therefore, a satisfactory durability of thetransmission is not always guaranteed where the transmission is usedunder hard conditions. The reason for this will be described withreference to FIGS. 14 through 17. When the toroidal type continuouslyvariable transmission is in operation, the power roller 8 is stronglycompressed between the input-side disk 2 and the output-side disk 4 asshown in FIG. 14. Accordingly, the center hole of the power roller 8 isdeformed to be elliptical as exaggeratedly illustrated in FIG. 15. Inthis state, the pivot shaft portion 23 of the displacement shaft 7 isstrongly thrust in the directions in which the input-side disk 2 and theoutput-side disk 4 are arranged.

[0033] When the power roller 8 is strongly compressed between theinput-side disk 2 and the output-side disk 4, a large force thrusts thepower roller 8 outwardly in the radial directions of the input-side disk2 and the output-side disk 4 when viewed in cross section, since theperipheral surfaces 8 a of the power roller 8 is engaged with the innersurface 2 a of the input-side disk 2 and the inner surface 4 a of theoutput-side disk 4. Due to the thrust forces, the trunnion 6 supportingthe power roller 8 on its inner surface is elastically deformed from theconfiguration shown in FIG. 16A to the configuration shown in FIG. 16B.Since the support shaft portion 22 of the displacement shaft 7 issomewhat offset from the center of the trunnion 6, the displacementshaft 7 is inclined by the elastic deformation of the trunnion 6. Theinclination of the displacement shaft 7 leads to partial contact of theouter circumferential surface of the pivot shaft portion 23 of thedisplacement shaft 7 with the needle rollers 45, 45 constituting theradial needle roller bearing 25. More particularly, as shown by obliquelattices in FIG. 17, rolling surfaces of the needle rollers 45, 45 arestrongly pressed against the outer circumferential surface of the pivotshaft portion 23.

[0034] The partial contact by the elastic deformation of the powerroller 8 and the partial contact by the inclination of the displacementshaft 7 are summed, so that load regions as indicated by obliquelattices in FIG. 18 appear in the pivot shaft portions 23. In those loadregions, large area pressure is applied from the rolling surfaces of theneedle rollers 45, 45 to the outer circumferential surfaces of the pivotshaft portions 23. The surface roughness of the rolling surface (theinner and outer raceway portions being in contact with the rollingsurfaces of the needle rollers 45, 45) of a general radial needle rollerbearing, used in a high speed region of 10,000 rpm or higher, is about0.4 μmRa. However, since the rolling surfaces of the needle rollers 45,45 are strongly contacted with the outer circumference surface of thepivot shaft portion 23 in the above load regions, an oil film is hard tobe formed on the contact portions when the surface roughness of theouter circumference surface is about 0.4 μmRa.

[0035] In the portions on which large area pressure exerts, a largeamount heat is generated according to the operation of the toroidal typecontinuously variable transmission. Those portions are also locatedclose to traction portions where the peripheral surfaces 8 a of thepower roller 8 are in contact with the inner surface 2 a of theinput-side disk 2 and the inner surface 4 a of the output-side disk 4.Elevation of temperature caused by the heat generated in the tractionportions is great. Accordingly, the heat-resistance of those portionsreceiving the large area pressure needs to be secured for securing asatisfactory durability of the displacement shaft 7.

[0036] In addition, in the conventional toroidal type continuouslyvariable transmission, the radial needle roller bearings 25 whichrotatably support the power rollers 8 around the pivot shaft portions 23of the displacement shafts 7, respectively, are not always satisfactoryin their durability. The reason for this will be described hereunder.

[0037] Where the toroidal type continuously variable transmission isused for a transmission unit of a motor vehicle, an automotive powerthat is output from the engine to the input shafts 15, 15 a istransmitted to the output-side disk 4, through the input-side disk 2,2A, 2B and the power rollers 8, 8. The toroidal type continuouslyvariable transmission may be considered in the form of the radial needleroller bearings 25, which support the power rollers 8, 8 around thepivot shaft portions 23, respectively. In this case, it is operated inan outer race rotating mode in which the power roller 8 having the outerraceway 55 revolves. A load applied to the thus radial needle rollerbearing 25 is a radial component of a force, that is, a traction force,applied to the traction portions of the power roller 8 supported by theradial needle roller bearing 25, viz., the contact portions where theinner surfaces 2 a of the input disks 2A and 2B and the inner surface 4a of the output-side disk 4 are in contact with the peripheral surfaces8 a of the power rollers 8.

[0038] The radial load applied to the radial needle roller bearing 25varies depending on the output power (in particular torque) of theengine and a changing state of the speed change ratio of the toroidaltype continuously variable transmission. In the case of a normalaspiration engine of the displacement volume of 2,000 to 3,000 cc, theradial load is approximately 500 to 700 kgf (5000 to 700N) under thecondition that the toroidal type continuously variable transmission isin a maximum deceleration state and a maximum torque input state. In thecase of the natural aspiration engine of 800 cc to 1500 cc indisplacement volume, it is approximately 200 to 400 kgf (2000 to 4000N)under the same condition as above.

[0039] The radial needle roller bearing 25 is capable of sufficientlyenduring such a radial load if it is under a general load loadingcondition. However, the power roller 8, which functions as the outerrace of the radial needle roller bearing 25, is repeatedly elasticallydeformed due to loads from the inner surface 2 a of the input-side disk2, 2A, 2B and the inner surface 4 a of the output-side disk 4.Therefore, an excessive area pressure acts on a part of the rollingcontact surface, and the durability of the power roller 8 is possiblylost. This will be described with reference to FIGS. 19 to 22.

[0040] When the toroidal type continuously variable transmission is inoperation, loads indicated by an arrow a in FIGS. 19 to 20 are impartedto two opposed positions on each of the power rollers 8, 8 from theinner surface 2 a of the input-side disk 2, 2A, 2B and the inner surface4 a of the output-side disk 4. As seen from FIGS. 19 to 20, those loadsare directed toward the positions on the power rollers 8, 8 closer tothe trunnions 6, 6. When the loads directed to the arrow a are increasedin value, the inside diameters of the power rollers 8, 8 are elasticallydeformed as exaggeratedly shown in FIG. 21, the outer raceway 55 isdeformed to be elliptical in cross section as exaggeratedly illustratedin FIG. 22. In this case, the amount of deformation of the outer raceway55 is not caused in the axial direction of the radial needle rollerbearing 25 and increases in quantity toward the trunnions 6, 6 withrespect to the radial direction thereof. At a specific portion in thecircumferential direction of the outer raceway 55, the elasticdeformation inwardly in the radial direction thereof is conducted twotimes during one turn of each power roller 8.

[0041] As the result of the elastic deformation of the outer raceway 55,the distance between the inner raceway 54 and the outer raceway 55 ofthe radial needle roller bearing 25 becomes narrower at two oppositepositions in the radial direction where it faces the inner surface 2 aof the input-side disk 2, 2A, 2B and the inner surface 4 a of theoutput-side disk 4, and it is close to the trunnion 6. At thosepositions, the needle rollers 45, 45 of the radial needle roller bearing25 are forcibly compressed between the inner raceway 54 and the outerraceway 55. As a result, an excessive area pressure, which is due to anedge load, is applied to parts of the inner raceway 54 and the outerraceway 55, which face the ends of the needle rollers 45, 45 (whenaxially viewed) The excessive area pressure causes early flaking-off onthose portions.

[0042] When the portions are damaged by such pressure-flaking, sound andvibration generated at the radial needle roller bearing 25 become large.As a result, sounds and vibrations generated by not only the toroidaltype continuously variable transmission having the radial needle rollerbearings assembled thereinto but also the transmission unit having thetoroidal type continuously variable transmission, are increased. Thisadversely affects the drive feeling of the vehicle having thetransmission unit. Further, when flakes separated from the traces enterinto the traction portion transmitting the automotive power, the areapressure excessively increases thereat. This possibly causes the damagessuch as the flaking in the early stage in the inner surface 2 a of theinput-side disk 2, 2A, 2B and the inner surface 4 a of the output-sidedisk 4, and the peripheral surfaces 8 a, 8 a of the power rollers 8, 8,which form the traction portion. Moreover, the strainer and the filtersmay be clogged with the flakes thus caused. This results in reduction ofthe discharge amount of the pump for supplying the lubricating oil, poorlubricating, and reduction of lifetime of other parts.

SUMMARY OF THE INVENTION

[0043] Accordingly, a first object of the present invention is toprovide a toroidal type continuously variable transmission in which theeccentric quantity between the support shaft portion and pivot shaftportion is optimized in value and hence good speed-ration changeperformance is ensured.

[0044] Further, a second object of the present invention is to provide atoroidal type continuously variable transmission with pivot shaftportions, which is high in durability and reliability by making it easyto form an oil film on the contact portions where the outercircumferential surfaces of the pivot shaft portions are contacted withthe rolling surfaces of the needle rollers, and by increasing thedurability of the displacement shaft including the pivot shaft portionthrough the improvement of the heat resistance of the outercircumferential surfaces of the pivot shaft portions.

[0045] Accordingly, an object of the present invention is to provide aninput disk unit of a toroidal type continuously variable transmissionwhich succeeds in solving the problems arising from the radial load ofthe radial needle roller bearings.

[0046] According to the first aspect of the present invention, there isprovided a toroidal type continuously variable transmission, including:at least one pair of disks, each one surface in the axial direction ofwhich has a concave surface being arcuate in cross section, the disksconcentrically disposed on each other and rotatably supportedindependent from each other in a state that the concave surfaces areopposed to each other; a trunnion swingable about a pivot shaft situatedat a torsional relation with respect to a center axis of the pair ofdisks, the trunnion having a circular hole formed in a directionperpendicular to the axial direction of the pivot shaft at a middleportion thereof; a displacement shaft including a support shaft portionand a pivot shaft portion that are parallel and eccentric to each other,the support shaft portion rotatably supported to the inner surface ofthe circular hole through a radial bearing, the pivot shaft portionbeing protruded from an inner surface of the middle portion of thetrunnion; a power roller having an arcuate convex surface on theperipheral surface thereof, the power roller nipped between the concavesurfaces of the pair of disks while being rotatably supported on anouter circumferential surface of the pivot shaft portion; and a thrustbearings located between the power roller and the inner surface of themiddle portion of the trunnions, wherein an eccentric quantity of thedisplacement shaft being a distance between the support shaft portionand the pivot shaft portion is within a range from 5 mm to 15 mm.

[0047] The toroidal type continuously variable transmission, like theconventional one, transmits a rotational force between the input-sidedisk and the output-side disk, and changes a rotational speed ratio ofthe input-side disk and the output-side disk by changing the inclinationangle of the trunnion.

[0048] In case of the continuously variable transmission of theinvention, the eccentric quantitie of the displacement shaft, whichsupports the power roller on the trunnion is controlled to be within apredetermined range. Therefore, the inclination angle of the trunnionand the power roller about the pivot shafts can exactly be adjusted inaccordance with the displacement quantity of the trunnion over the axialdirection of the pivot shaft. As a result, the rotational speed ratio ofthe input- and output-side disks can be accurately adjusted as desired,to thereby improve the speed change performances of the continuouslyvariable transmission.

[0049] According to the second aspect of the invention, there isprovided a toroidal type continuously variable transmission, including:at least one pair of disks, each one surface in the axial direction ofwhich has a concave surface being arcuate in cross section, the disksconcentrically disposed on each other and rotatably supportedindependent from each other in a state that the concave surfaces areopposed to each other; a trunnion swingable about a pivot shaft situatedat a torsional relation with respect to a center axis of the pair ofdisks, the trunnion having a circular hole formed in a directionperpendicular to the axial direction of the pivot shaft at a middleportion thereof; a displacement shaft including a support shaft portionand a pivot shaft portion that are parallel and eccentric to each other,the support shaft portion rotatably supported to the inner surface ofthe circular hole through a radial bearing, the pivot shaft portionbeing protruded from an inner surface of the middle portion of thetrunnion; a power roller having an arcuate convex surface on theperipheral surface thereof, the power roller nipped between the concavesurfaces of the pair of disks while being rotatably supported on anouter circumferential surface of the pivot shaft portion through aradial needle roller bearing; and a thrust bearings located between thepower roller and the inner surface of the middle portion of thetrunnions, wherein a portion of the outer circumferential surface of thepivot shaft portion contactable with the rolling surfaces of the needlerollers of the radial needle roller bearing has a smoothed surfacehaving a surface roughness of 0.2 μmRa or less, and formed bysuperfinishing.

[0050] Further, in the toroidal type continuously variable transmissionof the invention, the displacement shafts are made of steel, the outerperipheral surface of at least the pivot shaft portion of thedisplacement shaft is formed with a carbonitriding layer containing 0.8to 1.5 wt % of carbon and 0.05 to 0.5 wt % of nitrogen, and at least theouter peripheral surface is quenched and tempered after thecarbonitriding process thereof.

[0051] Further, in the continuously variable transmission, thedisplacement shafts are made of steel, and a carbonitriding layercontaining 0.8 to 1.5 wt % of carbon and 0.05 to 0.5 wt % of nitrogen isformed on a surface portion of the outer peripheral surface of at leastthe drive shaft of the displacement shaft, and following thecarbonitriding process, at least the surface portion is quenched andtempered.

[0052] The toroidal type continuously variable transmission, like theconventional one, transmits a rotational force between the input-sidedisk and the output-side disk, and changes a rotational speed ratio ofthe input-side disk and the output-side disk by changing the inclinationangle of the trunnion.

[0053] In the toroidal type continuously variable transmission accordingto the second aspect of the invention, an oil film is easy to form onthe contact portion where the outer peripheral surface of the pivotshaft portion is in contact with the rolling surfaces of the needlerollers of the radial needle roller bearing. The oil film formedeffectively prevents damages (e.g., early flaking) of the outerperipheral surface of the pivot shaft portions.

[0054] Since the carbonitriding layer is formed on the outer peripheralsurface of the pivot shaft portions, its heat resistance is high enoughto prevent the outer peripheral surface from damaging such as the earlyflakes. Moreover, according to a third aspect of the invention, there isprovided a toroidal type continuously variable transmission, including:first and second disks concentrically disposed on each other androtatably supported about a mutual central axis, the first and seconddisks respectively having arcuate concave surfaces, which are opposed toeach other; trunnions swingable about a pivot shaft situated at atorsional relation which does not intersect with the central axis and isa position perpendicular to the central axis; a displacement shaftdisposed on a middle portion of the trunnion and supported in such amanner as to project from an inner surface of the trunnion; and a powerroller disposed on an inner surface side of the trunnion and nippedbetween the first and second disks in such a manner as to be rotatablysupported on the periphery of the displacement shaft through a radialbearing; the peripheral surface of the power roller having an arcuateconvex surface contactable with the concave surfaces of the first andsecond disks, wherein the radial bearing is a radial needle rollerbearing with a retainer and a plurality of needle rollers, the needlerollers are crowned at both end portions in the axial direction thereof,and a crowning quantity of the needle roller is 0.15 to 0.65% of theouter diameter of the center portion of the needle roller in the axialdirection thereof at a position closer to the center portion side of theneedle roller from an end face thereof by 5 to 15 % of the axial lengthof the needle roller.

[0055] The toroidal type continuously variable transmission, like theconventional one, transmits a rotational force between the input-sidedisk and the output-side disk, and changes a rotational speed ratio ofthe input-side disk and the output-side disk by changing the inclinationangle of the trunnion.

[0056] In the continuously variable transmission accoding to the thirdaspect of the invention, proper amounts of crowning is applied to theneedle rollers of the radial needle roller bearings, which rotatablysupport the power rollers on the displacement shafts. Therefore, theinvention prevents excessive area pressure from being applied to thecomponent parts of the radial needle roller bearings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0057]FIG. 1 is a side view schematically showing a basic structure of aconventional toroidal type continuously variable transmission when it isin a maximum deceleration state;

[0058]FIG. 2 is a side view schematically showing the basic structure ofthe toroidal type continuously variable transmission when it is in amaximum acceleration state;

[0059]FIG. 3 is a partial cross sectional view showing a specificstructure of a conventional first toroidal type continuously variabletransmission towards which the invention is directed;

[0060]FIG. 4 is a cross sectional view taken on line IV-IV in FIG. 3;

[0061]FIG. 5 is a cross sectional view showing a main portion of theconventional toroidal type continuously variable transmission in whichpower rollers are in a free state;

[0062]FIG. 6 is a cross sectional view taken on line XI-XI in FIG. 5;

[0063]FIG. 7 is a cross sectional view showing a main portionincorporating a lubricating-oil supplying path thereinto;

[0064]FIG. 8 is a partial cross sectional view showing a specificstructure of a conventional second toroidal type continuously variabletransmission towards which the invention is directed;

[0065]FIG. 9 is a partial cross sectional view showing a specificstructure of a conventional third toroidal type continuously variabletransmission towards which the invention is directed;

[0066]FIG. 10 is a cross sectional view schematically showing thetoroidal type continuously variable transmission of FIG. 8 when it is ina maximum deceleration state;

[0067]FIG. 11 is an enlarged view showing an upper-left portion of FIG.10;

[0068]FIG. 12A is a sectional view showing a structure including atrunnion and a power roller when viewed in the direction of an arrow Bin FIG. 11 in a state that no power is transmitted;

[0069]FIG. 12B is a sectional view showing a structure including atrunnion and a power roller when viewed in the direction of an arrow Bin FIG. 11 in a state that large power is transmitted;

[0070]FIGS. 13A and 13B are diagrams for explaining a displacement ofthe center of rotation of the power roller in a state that large poweris transmitted;

[0071]FIG. 14 is a partial cross sectional view for explaining a loadapplied to the power roller when the toroidal type continuously variabletransmission is in operation;

[0072]FIG. 15 is a cross sectional view taken on line XV-XV in FIG. 14;

[0073]FIGS. 16A and 16B are cross sectional views showing a deformationof the trunnion when the toroidal type continuously variabletransmission is in operation;

[0074]FIG. 17 is a cross sectional view for explaining load regions ofthe pivot shaft portion caused by an inclination of the pivot shaft;

[0075]FIG. 18 is a diagram showing load regions of the pivot shaftportions caused by the inclination of the pivot shafts and deformationof the power rollers;

[0076]FIG. 19 is a cross sectional view for explaining loads applied tothe power rollers when the continuously variable transmission similar tothe structure shown in the FIG. 3 is in operation;

[0077]FIG. 20 is a cross sectional view for explaining loads applied tothe power rollers when the continuously variable transmission similar tothe structure shown in the FIG. 13 is in operation;

[0078]FIG. 21 is a cross sectional view showing a main portion of theconventional continuously variable transmission shown in the FIG. 5 in astate that the power roller is deformed;

[0079]FIG. 22 is a cross sectional view taken on line XXII-XXII in FIG.21;

[0080]FIG. 23 is a graph showing how the revolution of the pivot shaftaccording to an eccentric quantity of the displacement shaft affects adisplacement of the power roller in the axial direction of the pivotshaft according to a first embodiment of the invention;

[0081]FIGS. 24A and 24B are diagrams showing the displacement shaft whenviewed from the axial direction of the input-side disk and theoutput-side disk, for explaining a force acting on the displacementshaft during the power transmission;

[0082]FIG. 25 is a cross sectional view taken on line XXV-XXV in FIG. 8;

[0083]FIG. 26A and 26B are diagrams showing two specific displacementshafts, illustrated for the same purpose as of FIG. 24;

[0084]FIGS. 27A and 27B are views showing the relation of the eccentricquantities with the cross sectional areas and the moment of inertial ofarea of the joint portions, and the deformation quantities of thedisplacement shafts in the axial direction of the pivot shafts, relatingto the two displacement shafts shown in FIGS. 26A and 26B each havingthree different eccentric quantities;

[0085]FIG. 28 is a graph showing how the elastic deformation accordingto the eccentric quantity effects the displacement amount of thedisplacement shaft in the axial direction of the pivot shaft, relatingto the displacement shaft shown in FIG. 26A;

[0086]FIG. 29 is a graph showing how the elastic deformation accordingto the eccentric quantity effects the displacement amount of thedisplacement shaft in the axial direction of the pivot shaft, relatingto the displacement shaft shown in FIG. 26B;

[0087]FIG. 30 is a diagram showing second embodiment of a toroidal typecontinuously variable transmission according to the present invention,in which a displacement shaft is viewed from the same direction as inFIG. 4;

[0088]FIG. 31 is a cross sectional view showing a structure including apower roller and a thrust ball bearing according to the secondembodiment;

[0089]FIG. 32 is a cross sectional view showing a main portion of athird embodiment of the present invention, in which a power roller is ina free state;

[0090]FIG. 33 is a cross sectional view showing the power roller beingelastically deformed according to the third embodiment;

[0091]FIG. 34 is a cross sectional view taken on line XXXIV-XXXIV inFIG. 33;

[0092]FIG. 35 is a cross sectional view showing a needle roller of aradial needle roller bearing;

[0093]FIG. 36 is a graph showing a relationship between a durability ofthe radial needle roller bearing and a crowning quantity, obtained in afirst test; and

[0094]FIG. 37 is a graph showing a relationship between a durability ofthe radial needle roller bearing and a crowning quantity, obtained in asecond test.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0095] Some preferred embodiments of a toroidal type continuouslyvariable transmission constructed according to the present inventionwill be described with reference to the accompanying drawings.

[First Embodiment]

[0096] The toroidal type continuously variable transmission of a firstembodiment may be characterized in that an eccentric quantity L₇ betweenthe support shaft portion 22 and the pivot shaft portion 23,constituting the displacement shaft 7 for supporting the power roller 8with respect to the trunnion 6, is selected to be within a predeterminedrange of quantity values, whereby a rotational speed ratio of theinput-side disk 2 (2A, 2B) to the output-side disk 4 is set at a desiredone. The remaining structure of the continuously variable transmissionis substantially the same as of the conventional or proposed toroidaltype continuously variable transmission, which was already describedwith reference to FIGS. 3 through 8. For this reason, no furtherdescription and illustration of the structure will be given except someportions required for explanation of the invention. A description willbe given of the process that the inventor(s) discovered the fact thatwhen the eccentric quantity L₇ of the support shaft portion 22 withrespect to the pivot shaft portion 23 is selected to be within a rangefrom 5 to 15 mm, the rotational speed ratio can be set at a desired one.

[0097] The discovered fact is valid when a toroidal type continuouslyvariable transmission can be used for a transmission unit of a generalmotor vehicle, and when the component parts of the continuously variabletransmission have the following dimensions:

[0098] Outside diameters of input- and output-side disks 2(2A, 2B) and4:80 to 200 mm

[0099] Outside diameter of power roller 8:50 to 120 mm

[0100] Outside diameter of support shaft portion 22:10 to 40 mm

[0101] Outside diameter of pivot shaft portion 23:10 to 40 mm

[0102] Support length of power roller 8 when it is supported by pivotshaft portion 23 (=L₂₃ in FIG. 25, to be given later):10 to 40mm

[0103] Torque to be input into toroidal type continuously variabletransmission: 3 to 70 kg·m

[0104] A first attention was paid to how the eccentric quantity L₇affects an inclination angle of the power roller 8, which is directlylinked with the rotational speed ratio. To absorb dimensional toleranceof the component parts and the elastic deformations of those partsduring the power transmission, the pivot shaft portion 23 of thedisplacement shaft 7 revolves about the center of the support shaftportion 22 thereof, as shown in FIG. 13A, and the center of the pivotshaft portion 23 shifts from a point {circumflex over (1)} to anotherpoint {circumflex over (2)} of FIG. 13A. In this case, the center of thesupport shaft portion 22 is left at a point {circumflex over (3)} ofFIG. 13A. A displacement of the pivot shaft portion 23 produced when thepivot shaft portion 23 revolves about the support shaft portion 22 asshown in FIG. 13A can be analyzed with reference to FIG. 13B. In FIG.13B, L₇ is a quantity of an eccentricity of the pivot shaft portion 23from the support shaft portion 22; x₈ is a displacement of the powerroller 8 toward the output-side disk 4; and y₈ is a displacement of thepower roller 8 produced when it is displaced toward the pivot shaft 5,which pivotally supports the trunnion 6, in accordance with thedisplacing of the power roller 8 toward the output-side disk 4. In thechart of FIG. 13B, the following equation is established:

L ₇ ²=(L ₇ -y ₈)² +x ₈ ²

[0105] Rearranging the above equation for Y₈, then we have

y ₈ ²-2L ₇ y ₈ +x ₈ ²=0

[0106] A displacement Y₈ toward the pivot shaft 5 is given by

y ₈ L ₇-(L ₇ ²-x ₈ ²)

[0107] Design and test of various toroidal type continuously variabletransmissions of small power to large power were made. The experienceshows that in the case of the toroidal type continuously variabletransmissions for motor vehicles, when it is in a maximum decelerationstate and a maximum torque input state as already shown in FIG. 10, thedisplacement x₈ is within approximately 1.5 to 2.5 mm as the total ofthe dimensional tolerance and the elastic deformations of the componentparts of the continuously variable transmission. That is, thedisplacement x₈ in case of the continuously variable transmission forsmall power is substantially 1.5 mm, and the displacement x8 in case ofthe continuously variable transmission for large power is substantially2.5 mm. The value of the displacement x₈ is calculated from the elasticdeformation quantities of the component parts calculated by an FEManalysis, and it was confirmed through a measurement using an actuallyassembled toroidal type continuously variable transmission. In themeasurement, the outer surfaces (opposed to the power rollers 8) of theouter races 28, 28 (FIGS. 3 to 11) of the thrust ball bearings 26, 26,were blackening, and the toroidal type continuously variabletransmission was actually operated. The displacement x₈ was confirmedfrom the contact traces left on the outer surfaces, which result fromtheir contact with the thrust needle roller bearings 27, 27 (FIGS. 3, 4,10 and 11).

[0108] The displacement x₈ of the power roller 8 toward the output-sidedisk 4 is 1.5 to 2.5 mm as just mentioned. The quantities of thedisplacement y₈ caused by the displacement x₈ was calculated by use ofthe above equation, and the result of calculations is graphicallydepicted in FIG. 23. In the graph of FIG. 23, the quantities of thedisplacement y₈ are plotted about three displacements x₈ of 1.5 mm, 2.0mm and 2.5 mm. As seen from the graph, of the displacement x₈ beingwithin the range from 1.5 mm to 2.5 mm, the displacement y₈ increaseswhen the eccentric quantity L₇ is within 7 mm, irrespective of thevalues of the displacement x8. Particularly when the eccentric quantityL₇ is smaller than 5 mm, the displacement Y₈ has a large value. Fromthis, it is seen that to reduce the displacement y₈, the eccentricquantity L₇ is 5 mm or larger, preferably 7 mm or larger.

[0109] The eccentric quantity L₇ affects the rotational speed ratio ofthe input-side disk 2 (2A, 2B) to the output-side disk 4, in connectionwith the dimensions of an actual toroidal type continuously variabletransmission. Let us calculate the affection of the eccentric quantity.The following preconditions for the calculation were set up: 1) thedisplacement x₈ of the power roller 8 toward the output-side disk 4,based on the dimensional tolerance of the component parts and theelastic deformations of those parts, was 2 mm; 2) a fullspeed-change-ratio angle as a turn angle of the power roller 8 between amaximum acceleration position (FIG. 1) and a maximum decelerationposition (FIG. 2) was 60°; and 3) a cam lead of the precess cam was 45mm/360° in connection with the turn angle. It is general that the turnangle (full speed-change-ratio angle) of the power roller 8 is selectedto be within 50° to 70°, although it depends on the width of the speedchange ratio. A test, conducted by the company of the present patentapplication, showed that a preferable cam lead ranges 40 mm/360° to 60mm/360°.

[0110] With the above conditions, calculation about the affection of theeccentric quantity L₇ to the speed change ratio will be made. Tocalculate, it is assumed that the eccentric quantity L₇ is 3 mm. Whenthe power roller 8 is displaced 2 mm in the x-direction, the powerroller 8 displaces 0.764 mm in the y-direction with the revolution ofthe pivot shaft portion 23 about the support shaft portion 22. In thiscase, a turn angle of the trunnion 6 caused by the y-directionalmovement, i.e., a speed-change-ratio angle of the power roller 8, is(0.764/45)×360°=6.1120°. When this value is compared with 60° of thefull speed-change-ratio angle, then we have 6.1120°/60°=0.102. Thisfigure teaches that when the pivot shaft portion 23 revolves around thesupport shaft portion 22 to displace the power roller 8 in they-direction, the speed-change-ratio angle of the power roller 8 changesby 10.2% of the full speed-change-ratio angle. This figure, 10.2%, isvery large, and does not lead to the achievement of a desired speedchange ratio performance.

[0111] If the eccentric quantity L₇ is 10 mm, the power roller 8 moves0.202 mm in the y-direction under the same conditions as in the abovecase. A speed-change-ratio angle of the power roller 8 according to themovement is (0.202/45)×360°=1.616°. When this value is compared with thevalue of the full speed-change-ratio angle, then 1.616°/60°=0.027. Thisvalue is much smaller than that in the case of L₇=3 mm; a deviation ofthe speed-change-ratio angle is only 2.7%, and hence it leads to theachievement of a desired speed change ratio performance. Further, ifL₇=15 mm and L₇=20 mm, the displacements y₈ of the power roller in they-direction are 0.134 mm and 0.100 mm, and changing rates of thespeed-change-ratio angle are 1.8% and 1.3%. There is no great differencebetween the calculation result in the case of L₇=15 mm and that in thecase of L₇=20 mm. This fact teaches that increase of the eccentricquantity L₇ to a value in excess of 15 mm is insignificant in preservingthe speed change ratio performance by suppressing the displacement y₈ inthe y-direction.

[0112] Although the reason why the lower limit of the eccentric quantityL₇ is set at 5 mm, preferably 7 mm is as mentioned above, the upperlimit of the eccentric quantity L₇ will be described. The support shaftportion 22 of the displacement shaft 7 is supported by the radial needleroller bearings 24 within the annular holes 21, which is provided in themiddle portion of the trunnion 6. The displacement shaft 7 is supportedon the trunnion 6 in a cantilever fashion, as shown in FIG. 24A. Whenthe toroidal type continuously variable transmission is in operation, alarge force in an arrow direction of α of FIGS. 24A and 25 is applied tothe power rollers 8, 8, which is rotatably supported on the pivot shaftportion 23 of the displacement shaft 7, by means of the radial needleroller bearing 25. That is, a force, the direction of which is therotational direction of the input-side disk 2 (2A, 2B) is applied to thecontact portion where the inner surface 2 a of the input-side disk 2(2A, 2B) is in contact with the peripheral surfaces 8 a of the powerroller 8. A force, the direction of which is opposite to the rotationaldirection of the output-side disk 4 (i.e., the same as the rotationaldirection of the input-side disk 2) is applied to the contact portionwhere the inner surface 4 a of the output-side disk 4 is in contact withthe peripheral surfaces 8 a of the power roller 8. This force isapplied, as shown in an arrow direction of β in FIG. 24B, to the centerposition in the axial direction of the radial needle roller bearing 25on the center axis of the pivot shaft portion 23, so that the force actsto bend the displacement shaft 7. If the displacement shaft 7 has a lowrigidity, the displacement shaft 7 is greatly deformed, and the powerroller 8 supported on the displacement shaft 7 is easy to displace inthe arrow direction of a(substantially coincident with the y-direction).

[0113] On the other hand, a portion of the displacement shaft 7 wherethe rigidity is the lowest is the joint portion where the support shaftportion 22 is jointed to the pivot shaft portion 23. Increase of theeccentric quantity L₇ between the support shaft portion 22 and the pivotshaft portion 23 leads to reduction of the cross sectional area of thejoint portion and hence lowering of the rigidity in the joint portion.Where the eccentric quantity L₇ is small, the cross sectional area ofthe joint portion takes the shape of a perfect circle or similar to thesame. As the eccentric quantity L₇ increases, the cross sectional areabecomes elliptical in shape or is shaped like a rugby ball. Thus, withincrease of the eccentric quantity L₇, the cross sectional area changesits shape from the perfect circle to the ellipse or rugby ball. Themoment of inertia of area of the joint portion changes, so that adeformation of the displacement shaft 7, caused by the forces having thedirections of α and β, increases in its quantity. The fact that thisdeformation in the α and β directions is large leads to the fact thatthe contact points, where the peripheral surface 8 a of the power roller8 is in contact with the inner surface 2 a of the input-side disk 2 andthe inner surface 4 a of the output-side disk 4, are greatly moved inthe y-direction. It is desirable to reduce the quantities of thedeformation in the α and β directions as small as possible, as well asin the case of the displacement in the y-direction based on theeccentric quantity L₇.

[0114] Specific configurations and dimensions of the displacement shaft7 will be described. To this end, two examples of the displacement shaft7 are given in FIGS. 26A and 26B. The displacement shaft shown in FIG.26A is to be assembled into a toroidal type continuously variabletransmission for the engine of relatively small power, and thedisplacement shaft shown in FIG. 26B is to be assembled into a toroidaltype continuously variable transmission for the engine of relativelylarge power. In FIGS. 26A and 26B, numerals indicate the outsidediameters (in mm) of portions indicated by dimension lines. FIGS. 27Aand 27B show those two displacement shafts each having three differenteccentric quantities L₇, together with specific values of the crosssectional areas S(mm²) and the moment I of inertial of area of the jointportions, and the deformation quantities λ(mm) of the displacement shaft7 in the axial direction (y-direction) of the pivot shafts.

[0115] The deformation quantity λ of the displacement shaft 7 isexpressed by

λ=PL ₂₃ ³/(3EI)

[0116] In the above equation, P is a load applied to the displacementshaft 7. The load P corresponds to an automotive power transmittedthrough the power roller 8, i.e., a traction force. L₂₃ is a distancefrom a point of application to a fulcrum of the load P, viz., the lengthof an arm, and corresponds the length from the joint portion between thesupport shaft portion 22 and the pivot shaft portion 23 to the centerposition of the radial needle roller bearing 25 when viewed in the axialdirection. E is Young's modulus of a hard metal, e.g., bearing steel ofthe displacement shaft, and is 21000 kgf/mm². The distance L₂₃ (from theforce application point to the fulcrum) and the force P were 25 mm and250 kgf for the displacement shaft 7 for the small engine power shown inFIGS. 26A and 27A, and 30 mm and 600 kgf for the displacement shaft 7for the large engine power shown in FIGS. 26B and 27B.

[0117] Under the above-mentioned preconditions, calculation was made onthe deformation quantity λ of the displacement shaft 7 according to aninfluence of the eccentric quantity L₇. FIG. 28 shows a variation of thedeformation quantity λ of the displacement shaft 7 assembled into thetoroidal type continuously variable transmission for the small powerengine shown in FIG. 26A and 27A with respect to the eccentric quantityL₇. FIG. 29 shows a variation of the deformation quantity λ of thedisplacement shaft 7 assembled into the toroidal type continuouslyvariable transmission for the large power engine shown in FIG. 26B and27B with respect to the eccentric quantity L₇. As seen from FIGS. 28 and29, a curve representative of a variation of the deformation quantity λof the displacement shaft 7 rises when the eccentric quantity L₇ is 12mm or longer, irrespective of the size of the displacement shaft 7. Whenthe eccentric quantity L₇ is 15 mm or larger, the curve sharply rises.From this fact, it is seen that the upper limit of the eccentricquantity L₇ is 15 mm, preferably 12 mm.

[0118] From the analysis described above, it is concluded that if thedimensions of the toroidal type continuously variable transmission arewithin the above-mentioned ones, the eccentric quantity L₇ of the pivotshaft portion 23 of the displacement shaft 7 to the support shaftportion 22 thereof is selected to be within a range from 5 mm to 15 mm,irrespective of the magnitude of an automotive power (in particulartorque) transmitted by the toroidal type continuously variabletransmission, or the size of the displacement shaft 7. Thus, a variationof the speed change ratio, which is due to the dimensional tolerance ofthe component parts of the continuously variable transmission andelastic deformations caused by thrust loads applied during the powertransmission, can be reduced to such a variation level as to create noproblem in practical use.

[0119] As seen from the foregoing description, in the toroidal typecontinuously variable transmission constructed as mentioned above, itsspeed change ratio can be controlled to a desired one, and hence in amotor vehicle having the continuously variable transmission of theinvention assembled thereinto, the improvement of running performancesand efficient fuel consumption are both achieved.

[0120] [Second Embodiment]

[0121] Turning now to FIGS. 30 to 31, there is shown a second embodimentof the present invention. In this embodiment to be described hereunder,the invention is directed to the improvement of the displacement shafts7 for rotatably supporting the power rollers 8 on the trunnions 6 (FIGS.1 through 7). The remaining structure and operation of the continuouslyvariable transmission are substantially the same as of the conventionalor proposed toroidal type continuously variable transmission alreadydescribed. For this reason, a description and illustration of thesimilar structure will be omitted or simply given, and a feature of theinvention and a portion except for the above explained will be given.

[0122] As shown, the displacement shaft 7 includes a support shaftportion 22 and a pivot shaft portion 23, which are parallel to eachother but the former is eccentric from the latter. A flange portion 46is formed at a continuous portion where the support shaft portion 22 andthe pivot shaft portion 23 are continuous. The outside diameter D₄₇ of abase-side half part 47 of the pivot shaft portion 23, located closer tothe flange portion 46, is larger than the outside diameter D₄₈ of thetip-side half part 48 of the same (D₄₇>D₄₈). When the outside diameterD₄₇ of the base-side half part 47 of the pivot shaft portion 23 isincreased, the following advantages are produced. The cross section areaof the continuous portion between the support shaft portion 22 and thepivot shaft portion 23 is secured in a satisfactory level. A bendingrigidity of the continuous portion is increased. Therefore, thedisplacement shaft 7 is hard to bend at this continuous portion duringthe operation of the continuously variable transmission, and thedisplacement shaft 7 is less deformed when it is subject to heattreatment.

[0123] Further, in the base surface of the support shaft portion 22,i.e., its base surface located closer to the flange portion 46, there isformed a chamfered part 49 which is chamfered at a portion outwardlyprotruding from the outer peripheral surface of the flange portion 46 ofthe base surface in the radial direction of the support shaft portion22. The chamfered part 49 prevents the interference with the outer race28 of the thrust ball bearing 26 which supports the power roller 8, andprovides a smooth surface of the continuous portion between the supportshaft portion 22 and the flange portion 46. The smooth surfaceeliminates deformation of the displacement shaft 7 during its heattreatment. An inclination angle θ of the chamfered part 49 is preferablywithin a range from 10 to 45°.

[0124] On the other hand, there is formed a center hole 50 in thecentral portion of the outer race 28 of the thrust ball bearing 26 forsupporting the power roller 8, which is rotatably supported by thedisplacement shaft 7 as mentioned above. The center hole 50 can receivethe flange portion 46 and the base-side half part 47 in a fittingfashion without the rattling therebetween. The center hole 50 includes asmall-diameter portion 51 for receiving the base-side half part 47fittingly, and a large-diameter portion 52 for receiving the flangeportion 46 fittingly. The depth D₅₂ of the large-diameter portion 52 isslightly larger than the thickness T₄₆ of the flange portion 46(D₅₂>T₄₆) . With such dimensional selection, a part of the flangeportion 46 is not protruded out of the outer surface (upper surface inFIG. 31) of the outer race 28 when the flange portion 46 and the basepart 47 are fit into the center hole 50. This is needed in order toprevent the flange portion 46 from interfering with the thrust needleroller bearing 27 (FIGS. 3 through 7), which is located between theouter race 28 and the inner surface of the trunnion 6.

[0125] The power roller 8 is rotatably supported on the tip-side halfpart 48 of the pivot shaft portion 23 of the thus configureddisplacement shaft 7 by means of the radial needle roller bearing 25(FIGS. 4 through 7). A portion of the outer circumferential surface ofthe tip-side half part 48, that is, in the outer circumferential surfaceof the pivot shaft portion 23, a rolling surface of thereof with whichthe rolling surfaces of the needle rollers 45, 45 (shown in FIGS. 3 to7, and FIGS. 14 and 15) of the radial needle roller bearing 25 arebrought into contact is smoothed to have a surface roughness of 0.2 μmRaor less, by superfinishing. Grinding finishing, not superfinishing, canproduce within 0.2 μmRa (surface roughness); however, grinding techniqueis difficult, and its cost is high. In this respect, use of thesurperfinishing is preferable. The displacement shaft 7 is made ofsteel, for example, chromium-molybdenum steel (e.g., SCM 435 (JIS G4105)) or high-carbon-chromium bearing steel (e.g., SUJ 2 (JIS G4805)) Acarbonitriding layer containing 0.8 to 1.5 wt % of carbon and 0.05 to0.5 wt % of nitrogen is formed on a surface portion (actually, theentire surface of the displacement shaft 7) of the outer peripheralsurface of at least the lower part 48 of the displacement shaft 7 madeof steel. Following the carbonitriding process, at least the surfaceportion (actually the entire surface of the displacement shaft 7) isquenched and tempered, so as to increase the hardness of the surfaceportion to HRc60 or higher.

[0126] In the thus constructed toroidal type continuously variabletransmission, an oil film is easy to form on the contact portion wherethe outer peripheral surface of the lower part 48 of the pivot shaftportion 23 is in contact with the rolling surfaces of the needle rollers45, 45 of the radial needle roller bearing 25. And, the formed oil filmprevents damages (e.g., early flaking) of the outer peripheral surfaceof the tip-side half part 48. Table 1 shows the results of an endurancetest, conducted by the inventor(s). The test was conducted to know howthe surface roughness of the outer peripheral surface of the tip-sidehalf part 48 affects the lifetime of the outer peripheral surfacethereof. Samples 1 to 8 were tested under the same conditions which areother than the surface roughness of the outer peripheral surface of thetip-side half part 48; the material, carbon density, and nitrogendensity are the same as of sample 4 in Table 2 to be given later, andsurface hardness is HRc62. TABLE 1 Surface roughness of the outersurface of the tip-side half super- Judge- No. part [μmRa] finishingTest result ment 1 1.0 no Rolling surface/needle outer X surface flakedafter 10 hr 2 0.6 no Rolling surface flaked after X 71 hr 3 0.6 noRolling surface/needle outer X surface flaked after 64 hr 4 0.5 noRolling surface flaked after X 111 hr 5 0.4 yes Rolling surface flakedafter X 209 hr 6 0.2 yes No problem after 250 hr ◯ 7 0.2 yes No problemafter 250 hr ◯ 8 0.1 yes No problem after 250 hr ◯

[0127] The test results show that the outer surface of the lower part 48is not damaged (not suffered from early flaking, for example) if theouter surface is superfinished to have 0.2 μmRa or less in surfaceroughness. The surface roughness of the surface other than the tip-sidehalf part 48 does not need to finish smoothly as that of the tip-sidehalf part 48. Approximately 1.6 μmRa is satisfactory for the surfaceroughness of its outer surface since the support shaft portion 22 isjust supported on the trunnion 6 so as to allow its slight pivotingdisplacement.

[0128] Since the carbonitriding layer is formed on the surface portionof the outer peripheral surface of at least the tip-side half part 48 ofthe pivot shaft portion 23, its heat resistance is high enough toprevent the outer peripheral surface from suffering from early flakes.To know how the carbon and nitrogen contents (densities) of thecarbonitriding layer formed in the surface portion of the lower part 48affects the lifetime of the outer peripheral surface, an endurance testwas conducted. The test results are shown in Table 2. In testing samples1 to 7, other conditions than the carbon and nitrogen contents(densities) of the carbonitriding layer formed in the outer peripheralsurface of the tip-side half part 48 were equal; the finished sample 6in Table 1 was used. TABLE 2 Carbon Nitrogen Judge- No. Material density% density % Test results ment 1 SCM420 0.78 0.21 Flakes after 171 hr X 2SCM435 0.96 0.02 Flakes after 201 hr X 3 SCM435 0.83 0.25 No problemafter ◯ 250 hr 4 SCM420 1.08 0.06 No problem after ◯ 250 hr 5 SUJ2 1.410.46 No problem after ◯ 250 hr 6 SUJ2 1.00 0.00 Flakes after 163 hr X 7SUJ2 1.53 0.32 Flakes after 142 hr X

[0129] The toroidal type continuously variable transmission thusconstructed succeeds in preventing the peripheral surfaces of the pivotshaft portions of the displacement shafts for supporting the powerrollers to the trunnions from damaging, e.g., flaking in early stage.Therefore, the durability and reliability of the continuously variabletransmission are improved.

[0130] [Third Embodiment]

[0131] A third embodiment of the present invention will be describedwith reference to FIGS. 32 to 35. In the embodiment, the presentinvention is directed to the improvement of the radial needle rollerbearings 25 a for rotatably supporting the power rollers 8 on theperiphery of the pivot shaft portions 23 constituting the displacementshafts 7 in a toroidal type continuously variable transmission. Theremaining structure and operation of the continuously variabletransmission are substantially the same as of the conventional orproposed toroidal type continuously variable transmission alreadydescribed. For this reason, a description and illustration of thesimilar structure will be omitted or simply given. The description ofthe embodiment will be made placing emphasis on its feature.

[0132] Each radial needle roller bearing 25 a is constructed with aplurality of needle rollers 45 a, 45 a and a cage-like window typeretainer 53 for retaining rollably those needle rollers 45, 45. In thiscase, the outer circumferential surface of the pivot shaft portion 23serves as the cylindrical inner raceway 54 of the radial needle rollerbearing 25, and the inner circumferential surface of the power roller 8serves as the outer raceway 55 of the radial needle roller bearing 25.

[0133] In case of the toroidal type continuously variable transmission,as well shown in FIG. 35, both ends of the needle roller 45 a (whenviewed axially) are tapered to have crownings 68, 68. A crowningquantity δ₆₈ of the needle roller 45 a, viz., a distance (radiallyranges) of the outer surface of the crowning 68 from the outercircumferential surface of the needle roller 45 a (assumed by extendingstraight from the outer surface of the cylindrical portion 69, which isprovided in the center portion of the needle roller 45 a in the axialdirection thereof), is determined in the following way. It is assumedthat the axial length of the needle roller 45 a is L_(45a), the outerdiameter of the cylindrical portion 69 is D₆₉, and a distance from eachend face of the needle roller 45 a to a measuring point of the crowningquantity δ₆₉ is L₆₈. Further, it is assumed that the distance L₆₈ to themeasuring point is selected to be 5 to 15% of the axial length L_(45a);L_(45a)=(0.05 to 0.15)×L_(45a). Under this conditions, the crowningquantity δ₆₈ is selected to be 0.15 to 0.65% of the outer diameter D₆₉of the cylindrical portion 69; δ₆₈=(0.0015 to 0.0065)×D₆₉.

[0134] In the toroidal type continuously variable transmission of theembodiment, the needle rollers 45 a of radial needle roller bearing 25 afor rotatably supporting the power roller 8 to the pivot shaft portions23 of the displacement shafts 7 are crowned (designated by numeral 68)with a proper crowning quantity. Therefore, even when the power rollers8 receives large thrust loads during the operation of the continuouslyvariable transmission and are elastically deformed, and as a result, thespace width between the inner raceway 54 and the outer raceway 55 of theradial needle roller bearing 25 a loses its uniformity, the crowning ofthe needle rollers 45 a effectively prevents excessive area pressurefrom being applied to the component parts of the radial needle rollerbearing 25 a.

[0135] That is, during the operation of the toroidal type continuouslyvariable transmission, the power roller 8 receives large thrust forcesat two positions thereon, radially opposite to each other, from theinner surface 2 a of the input-side disk 2 and the inner surface 4 a ofthe output-side disk 4 (shown in FIGS. 1 to 3, 8, 9, 19 and 20), andelastically deforms as exaggeratedly illustrated in FIGS. 33 and 34.However, even if the power roller 8 is thus elastically deformed to losethe uniformity of the space width between the inner raceway 54 and theouter raceway 55, the ends of the needle rollers 45 a do not come incontact with the inner raceway 54 and the outer raceway 55. Accordingly,the continuously variable transmission of the embodiment is preventedfrom the early flaking caused by the edge load.

[0136] As described above, both ends of each needle roller 45 a (whenviewed axially viewed) of the radial needle roller bearing 25 a areproperly crowned (designated as numeral 68). The crowning prevents theoccurrence of the edge loading, to thereby improve the durability of theradial needle roller bearing 25 a. When the outer raceway 55 structuredby the inner circumferential surface of the power roller 8 iselastically deformed, the needle rollers 45 a retained by the retainers53 somewhat change their attitude, so that the rolling surfaces of theneedle rollers 45 a, 45 provide the inner raceway 54 and the outerraceway 55. Contact of the rolling surfaces of the needle rollers 45 a,45 a with the inner raceway 54 and the outer raceway 55 is put in aproper contact state, to thereby suppress an excessive increase of thearea pressure on the contact portions.

[0137] In this connection, when the crowning quantity δ₆₈ is too small,generation of the edge load is insufficiently suppressed. In this case,the durability of the radial needle roller bearing 25 a isinsufficiently improved. On the contrary, when it δ₆₈ is too large, theneedle rollers 45 a, 45 a of the radial needle roller bearing and thepower roller 8 supported by the radial needle roller bearing 25 a areslanted. The result has an opposite effect that the edge load is easy togenerate and the early flaking is easy to occur. In addition, since thepower roller 8 transmits the automotive power while rotating at highspeed in a state that the power roller 8 is slanted compared with thenormal attitude, to thereby generate large sound and vibrations. Thewhole transmission with the transmission unit containing the toroidaltype continuously variable transmission generates large sound andvibrations, and thus, this adversely affects the drive feeling of thevehicle having the transmission unit.

[0138] On the other hand, in the present invention, the crowningquantity (δ₆₈ is controlled as described above, and hence the generationof the edge load is not prevented, and the power rollers 8 are notslanted during the operation of the continuously variable transmission.

[0139] A test conducted by the inventor(s) to set the crowning quantityδ₆₈ as described above will be described. High speed endurance tests wasperformed by use of a motor dynamo for two toroidal type continuouslyvariable transmissions for small engine power and for large enginepower.

[0140] As the toroidal type continuously variable transmission for largeengine power, a double cavity type toroidal type continuously variabletransmission of which the cavity diameter D₀ is 130 mm (cavity diameterD₀=distance between the pivot shafts 5, 5 provided at both ends of thetrunnions 6, 6, FIG. 4) was used. The operating conditions in the testwere: the number of revolutions each of the input-side disks 2A and 2Bwas 4000 rpm; input torque was 300 Nm; and the speed change ratio was0.5 (the number of revolutions of the output-side disk 4 was ½ of thatof the input disks). Dimensions of the radial needle roller bearing 25 awere: the diameter of an inscribed circle of each needle roller 45 a was25 mm; the diameter of a circumscribed circle was 33 mm (outsidediameter of the cylindrical portion 59 of the needle roller 45 a was 4mm); and the axial length L_(45a) of the needle roller 45 a was 16.8 mm.

[0141] Under the conditions the above-mentioned, a test for confirmingthe durability of the radial needle roller bearing 25 a was conductedwhile varying the crowning quantity δ₆₈ of the needle rollers 45 (thatis, using the crowning quantity δ₆₈ as a parameter), and thus, propercrowning quantities δ₆₈ could be obtained from the test. In advance ofhigh speed endurance test, an elastic deformation quantity of the powerroller 8 wad calculated on the basis of the values of the load appliedfrom the input- disk 2 and output-side disk 4 to the power roller 8during the operation of the continuously variable transmission, by anFEM process. The deformation quantity obtained was considered into thecrowning quantity δ₆₈. A target time for the high speed endurance testwas set at 200 hours. The value of 200 hours may be used as a referencevalue for endurance for the lifetime of the transmission unit of thevehicular transmission.

[0142] The test results are shown in Table 3 and FIG. 36. TABLE 3Crowning quantity δ₆₈ at a position distance 2 mm Test from the end ofthe No. needle roller Test results A No crowning The rolling surface ofthe needle roller & the inner race flake after 32 and 45 hours,respectively. B 0.002 mm The rolling surface of the needle roller & theinner race flake after 78 and 96 hours, respectively. C 0.004 mm Therolling surface of the needle roller & the inner race flake after 164and 135 hours, respectively. D 0.006 mm Test was over 200 hours andterminated after 250 hours, and no flake. The test was conducted twotimes. E 0.015 mm Test was over 200 hours and terminated after 250hours, and no flake. The test was conducted two times. F 0.026 mm Testwas over 200 hours and terminated after 250 hours, and no flake. Thetest was conducted two times. G 0.028 mm The rolling surface of theneedle roller & the inner race flake after 189 and 172 hours,respectively. H 0.035 mm The rolling surface of the needle roller & theinner race flake after 62 and 39 hours, respectively. Levels of soundand vibration were large.

[0143] The toroidal type continuously variable transmission being thesmall single cavity type of which the cavity diameter D₀ is 104 mm wassubjected to the high speed endurance test. The operating conditions inthe test were: the number of revolutions of the input-side disk 2 was4000 rpm; input torque was 60 Nm; and the speed change ratio was 0.5.Dimensions of the radial needle roller bearing 25 a were: the diameterof an inscribed circle of each needle roller 45 a was 16 mm; thediameter of a circumscribed circle was 20mm (outside diameter of thecylindrical portion 69 of the needle roller 45 a was 2 mm); and theaxial length L_(45a) was 13.8 mm.

[0144] The test results are shown in Table 4 and FIG. 37. TABLE 4Crowning quantity δ₆₈ at a position distance 1.5 mm Test from the end ofthe No. needle roller Test results A No crowning The rolling surface ofthe needle roller & the inner race flake after 21 and 16 hours,respectively. B 0.002 mm The rolling surface of the needle roller & theinner race flake after 92 and 129 hours, respectively. C 0.003 mm Testwas over 200 hours and terminated after 250 hours, and no flake. Thetest was conducted two times. D 0.007 mm Test was over 200 hours andterminated after 250 hours, and no flake. The test was conducted twotimes. E 0.013 mm Test was over 200 hours and terminated after 250hours, and no flake. The test was conducted two times. F 0.015 mm Therolling surface of the needle roller & the inner race flake after 148and 117 hours, respectively. G 0.022 mm The rolling surface of theneedle roller & the inner race flake after 85 and 68 hours,respectively. Levels of sound and vibration were large.

[0145] As seen from the test results, when the outside diameter of thecylindrical portion 69 of the needle roller 45 a is 4 mm, a targetdurability is secured in a condition that the crowning quantity δ₆₈ iswithin the range from 0.006 mm to 0.026 mm. When it is 2 mm, the targetdurability is secured in a condition that the crowning quantity δ₆₈ iswithin 0.003 mm to 0.013 mm. In those cases, to secure a satisfactorydurability, the crowning quantity δ₆₈ must be 0.15% to 0.65% of theoutside diameter D₆₉ of the cylindrical portion 69 of the needle roller45 a. The crowning quantity δ₆₈ was measured at a position closer to thecenter of the needle roller 45 a (axially viewed) by 5 to 15% of theaxial length L_(45a) of the needle roller 45 a, measured from the endface thereof. In the actual endurance test, the measuring point wasdistanced 2 mm (11.9%) from the end face of the needle roller when theaxial length L_(45a) is 16.8 mm (outside diameter=4 mm). It wasdistanced 1.5 mm (10.9%) from the end face of the needle roller when theaxial length L_(45a) is 13.8 mm (outside diameter=2 mm). In sample Ewhere the axial length L_(45a) is 16.8 mm (outside diameter=4 mm), thecrowning quantity was 0.011 mm (0.275%) at a position distanced 2.5 mm(14.9%) from the end face. The crowning quantity was also 0.023 mm(0.58%) at a position distanced 0.9 mm (5.4%) from the end face. Thosefigures satisfy the conditions set forth in claim. In sample D where theaxial length L_(45a) is 13.8 mm, the crowning quantity was 0.005 mm(0.25%) at a position distanced 2.0 mm (14.5%) from the end face. Thecrowning quantity was also 0.010 mm (0.5%) at a position distanced 0.7mm (5.1%) from the end face. The conditions set forth in claim aresatisfied in those figures.

[0146] When an initial radial gap of the radial needle roller bearing 25a is set to be large, a slant of the power roller 8 to the pivot shaftportion 23 of the displacement shaft 7 is large, to thereby causeunpleasant sound and vibrations during the operation of the toroidaltype continuously variable transmission. Further, due to a variation andthe reversal of the torque to be transmitted by the continuouslyvariable transmission (reversal : switching of the driving state to andfrom an engine braking state), the power roller 8 is repeatedly biasedto one side (when viewed in the radial direction) by a distancecorresponding to the radial gap. This results in increasing anunresponsive zone (where the speed change is not conducted even if aspeed change signal is input), and this phenomenon causes a disadvantagein the speed change control.

[0147] For this reason, it is preferable that the actual radial gap,while somewhat considering the deformation quantity of the power rollers8, is somewhat larger than a gap recommended for the radial needleroller bearing constructed with the needle rollers 45 a, 45 a and theretainer 53 (cage and roller), written in a catalog of those componentparts. In a case that the outside diameter (diameter of the innerraceway 54) of the pivot shaft portion 23 of the displacement shaft 7 is15 to 30 mm and the inside diameter (diameter of the outer raceway 55)of the power roller 8 is 20 to 40 mm, a preferable radial gap in theinitial stage (the power roller 8 being free) is approximately 0.020 to0.055 mm in diameter. For this values, the recommended gap according tocatalog are approximately 0.08 to 0.035 mm.

[0148] To prevent the early flaking, it is preferable that the surfaceroughness of the contact portions in contact with the rolling surfacesof the needle rollers 45 a is set to be good. The catalog recommendsthat the surface roughness Rmax of the outer peripheral surface (innerraceway 54) of the pivot shaft portion 23 of the displacement shaft 7 is1.6S, and the surface roughness Rmax of the inner peripheral surface(outer race 54) of the power roller 8 is 3.2S. It is preferable thatthose actual surface roughness are set to be somewhat smaller than therecommended ones (smoother). The surface hardness of the inner raceway54 and the outer raceway 55 is set to be substantially equal to that ofthe rolling surfaces of the needle rollers 45 a, 45 a, set at HRc60 orhigher as recommended in the catalog.

[0149] With thus structured and operated toroidal type continuouslyvariable transmission, the invention can provide an excellent durabilitythereof, and thus, promote the practical use of the toroidal typecontinuously variable transmission.

[0150] The present disclosure relates to the subject matter contained inJapanese patent application Nos. Hei. 10-6791 filed on Jan. 16, 1998,Hei. 10-11661 filed on Jan. 23 and Hei. 11-3646 filed on Jan. 11, 1999which are expressly incorporated herein by reference in its entirety.

[0151] While only certain embodiments of the invenoin have beenspecifically described herein, it will apparent that numerousmodifications may be made thereto without departing from the spirit andscope of the invention.

What is claimed is:
 1. A toroidal type continuously variabletransmission, comprising: at least one pair of disks, each one surfacein the axial direction of which has a concave surface being arcuate incross section, said disks concentrically disposed on each other androtatably supported independent from each other in a state that saidconcave surfaces are opposed to each other; a trunnion swingable about apivot shaft situated at a torsional relation with respect to a centeraxis of said pair of disks, said trunnion having a circular hole formedin a direction perpendicular to the axial direction of the pivot shaftat a middle portion thereof; a displacement shaft including a supportshaft portion and a pivot shaft portion that are parallel and eccentricto each other, said support shaft portion rotatably supported to theinner surface of said circular hole through a radial bearing, said pivotshaft portion being protruded from an inner surface of the middleportion of said trunnion; a power roller having an arcuate convexsurface on the peripheral surface thereof, said power roller nippedbetween said concave surfaces of said pair of disks while beingrotatably supported on an outer circumferential surface of said pivotshaft portion; and a thrust bearings located between said power rollerand the inner surface of the middle portion of said trunnions, whereinan eccentric quantity of said displacement shaft being a distancebetween said support shaft portion and said pivot shaft portion iswithin a range from 5 mm to 15 mm.
 2. A toroidal type continuouslyvariable transmission according to claim 1 , wherein said power rolleris rotatably supported on the outer circumferential surface of saidpivot shaft portion through a radial needle roller bearing, and aportion of the outer circumferential surface of said pivot shaft portioncontactable with the rolling surfaces of needle rollers of said radialneedle roller bearing has a smoothed surface having a surface roughnessof 0.2 μmRa or less, and formed by superfinishing.
 3. A toroidal typecontinuously variable transmission according to claim 1 , wherein saiddisplacement shafts are made of steel, the outer peripheral surface ofat least said pivot shaft portion of said displacement shaft is formedwith a carbonitriding layer containing 0.8 to 1.5 wt % of carbon and0.05 to 0.5 wt % of nitrogen, and at least the outer peripheral surfaceis quenched and tempered after the carbonitriding process thereof.
 4. Atoroidal type continuously variable transmission according to claim 1 ,wherein said power roller is rotatably supported through a radial needleroller bearing with a retainer and a plurality of needle rollers, saidneedle rollers are crowned at both end portions in the axial directionthereof, and a crowning quantity of said needle roller is 0.15 to 0.65%of the outer diameter of the center portion of said needle roller in theaxial direction thereof at a position closer to the center portion sideof said needle roller from an end face thereof by 5 to 15% of the axiallength of said needle roller.
 5. A toroidal type continuously variabletransmission, comprising: at least one pair of disks, each one surfacein the axial direction of which has a concave surface being arcuate incross section, said disks concentrically disposed on each other androtatably supported independent from each other in a state that saidconcave surfaces are opposed to each other; a trunnion swingable about apivot shaft situated at a torsional relation with respect to a centeraxis of said pair of disks, said trunnion having a circular hole formedin a direction perpendicular to the axial direction of the pivot shaftat a middle portion thereof; a displacement shaft including a supportshaft portion and a pivot shaft portion that are parallel and eccentricto each other, said support shaft portion rotatably supported to theinner surface of said circular hole through a radial bearing, said pivotshaft portion being protruded from an inner surface of the middleportion of said trunnion; a power roller having an arcuate convexsurface on the peripheral surface thereof, said power roller nippedbetween said concave surfaces of said pair of disks while beingrotatably supported on an outer circumferential surface of said pivotshaft portion through a radial needle roller bearing; and a thrustbearings located between said power roller and the inner surface of themiddle portion of said trunnions, wherein a portion of the outercircumferential surface of said pivot shaft portion contactable with therolling surfaces of said needle rollers of said radial needle rollerbearing has a smoothed surface having a surface roughness of 0.2 μmRa orless, and formed by superfinishing.
 6. A toroidal type continuouslyvariable transmission according to claim 5 , wherein said displacementshafts are made of steel, the outer peripheral surface of at least saidpivot shaft portion of said displacement shaft is formed with acarbonitriding layer containing 0.8 to 1.5 wt % of carbon and 0.05 to0.5 wt % of nitrogen, and at least the outer peripheral surface isquenched and tempered after the carbonitriding process thereof.
 7. Atoroidal type continuously variable transmission according to claim 5 ,wherein an eccentric quantity of said displacement shaft being adistance between said support shaft portion and said pivot shaft portionis within a range from 5 mm to 15 mm.
 8. A toroidal type continuouslyvariable transmission according to claim 5 , wherein said power rolleris rotatably supported through a radial needle roller bearing with aretainer and a plurality of needle rollers, said needle rollers arecrowned at both end portions in the axial direction thereof, and acrowning quantity of said needle roller is 0.15 to 0.65% of the outerdiameter of the center portion of said needle roller in the axialdirection thereof at a position closer to the center portion side ofsaid needle roller from an end face thereof by 5 to 15% of the axiallength of said needle roller.
 9. A toroidal type continuously variabletransmission, comprising: at least one pair of disks, each one surfacein the axial direction of which has a concave surface being arcuate incross section, said disks concentrically disposed on each other androtatably supported independent from each other in a state that saidconcave surfaces are opposed to each other; a trunnion swingable about apivot shaft situated at a torsional relation with respect to a centeraxis of said pair of disks, said trunnion having a circular hole formedin a direction perpendicular to the axial direction of the pivot shaftat a middle portion thereof; a displacement shaft including a supportshaft portion and a pivot shaft portion that are parallel and eccentricto each other, said support shaft portion rotatably supported to theinner surface of said circular hole through a radial bearing, said pivotshaft portion being protruded from an inner surface of the middleportion of said trunnion; a power roller having an arcuate convexsurface on the peripheral surface thereof, said power roller nippedbetween said concave surfaces of said pair of disks while beingrotatably supported on an outer circumferential surface of said pivotshaft portion through a radial needle roller bearing; and a thrustbearings located between said power roller and the inner surface of themiddle portion of said trunnions, wherein said displacement shafts aremade of steel, the outer peripheral surface of at least said pivot shaftportion of said displacement shaft is formed with a carbonitriding layercontaining 0.8 to 1.5 wt % of carbon and 0.05 to 0.5 wt % of nitrogen,and at least the outer peripheral surface is quenched and tempered afterthe carbonitriding process thereof.
 10. A toroidal type continuouslyvariable transmission according to claim 9 , wherein a portion of theouter circumferential surface of said pivot shaft portion contactablewith the rolling surfaces of needle rollers of said radial needle rollerbearing has a smoothed surface having a surface roughness of 0.2 μmRa orless, and formed by superfinishing.
 11. A toroidal type continuouslyvariable transmission according to claim 9 , wherein an eccentricquantity of said displacement shaft being a distance between saidsupport shaft portion and said pivot shaft portion is within a rangefrom 5 mm to 15 mm.
 12. A toroidal type continuously variabletransmission according to claim 9 , wherein said radial needle rollerbearing includes a retainer and a plurality of needle rollers, saidneedle rollers are crowned at both end portions in the axial directionthereof, and a crowning quantity of said needle roller is 0.15 to 0.65%of the outer diameter of the center portion of said needle roller in theaxial direction thereof at a position closer to the center portion sideof said needle roller from an end face thereof by 5 to 15% of the axiallength of said needle roller.
 13. A toroidal type continuously variabletransmission, comprising: first and second disks concentrically disposedon each other and rotatably supported about a mutual central axis, saidfirst and second disks respectively having arcuate concave surfaces,which are opposed to each other; trunnions swingable about a pivot shaftsituated at a torsional relation which does not intersect with thecentral axis and is a position perpendicular to the central axis; adisplacement shaft disposed on a middle portion of said trunnion andsupported in such a manner as to project from an inner surface of saidtrunnion; and a power roller disposed on an inner surface side of saidtrunnion and nipped between said first and second disks in such a manneras to be rotatably supported on the periphery of said displacement shaftthrough a radial bearing; the peripheral surface of said power rollerhaving an arcuate convex surface contactable with said concave surfacesof said first and second disks, wherein said radial bearing is a radialneedle roller bearing with a retainer and a plurality of needle rollers,said needle rollers are crowned at both end portions in the axialdirection thereof, and a crowning quantity of said needle roller is 0.15to 0.65% of the outer diameter of the center portion of said needleroller in the axial direction thereof at a position closer to the centerportion side of said needle roller from an end face thereof by 5 to 15%of the axial length of said needle roller.
 14. A toroidal typecontinuously variable transmission according to claim 13 , wherein saiddisplacement shaft includes a support shaft portion and a pivot shaftportion being arranged to be parallel to each other and eccentric toeach other, and an eccentric quantity of each said displacement shaftbeing a distance between said support shaft portion and said pivot shaftportion is within a range from 5 mm to 15 mm.
 15. A toroidal typecontinuously variable transmission according to claim 14 , wherein saidpower rollers are rotatably supported around the periphery of said pivotshaft portion through said radial needle roller bearing, and wherein aportion of the outer circumferential surface of said pivot shaft portioncontactable with the rolling surfaces of said needle rollers of saidradial needle roller bearing has a smoothed surface having a surfaceroughness of 0.2 μmRa or less, and formed by superfinishing.
 16. Atoroidal type continuously variable transmission according to claim 14 ,wherein said power rollers are rotatably supported around the peripheryof said pivot shaft portion through said radial needle roller bearing,said displacement shafts are made of steel, the outer peripheral surfaceof at least said pivot shaft portion of said displacement shaft isformed with a carbonitriding layer containing 0.8 to 1.5 wt % of carbonand 0.05 to 0.5 wt % of nitrogen, and at least the outer peripheralsurface is quenched and tempered after the carbonitriding processthereof.
 17. A toroidal type continuously variable transmissionaccording to claim 1 , wherein a maximum diameter each of said disks is80 to 200 mm, a maximum diameter of said power roller is 50 to 120 mm, adiameter of said support shaft portion is 10 to 40 mm, a diameter ofsaid pivot shaft portion is 10 to 40 mm, a distance in the axialdirection of said displacement shaft between a joint portion of saidsupport shaft portion and said pivot shaft portion, and an intermediateposition of said radial needle roller bearing is 10 to 40 mm, and torqueto be input into the toroidal type continuously variable transmission is3 to 70 kg·m.